1. Field of the Invention
The present invention relates to an operation command apparatus for use with a transistorized inverter which controls the frequency of a three-phase induction motor.
2. Description of Prior Art
FIG. 10 is a schematic block diagram of a conventional inverter operation command apparatus, wherein the numeral 1 indicates a transistorized inverter unit, 20 represents a controlling microprocessor, 30 designates operation keys consisting of a monitor switching key, a forward rotation key, a reverse rotation key, a stop key, an increase key, a decrease key, etc., 4 denotes a frequency display device, 7 indicates an operation command signal, 8 designates a frequency setting signal, 9 denotes an output frequency signal, and 10 represents a control power supply.
Operation will now be described. The signals of the various operation keys 30 are entered into the controlling microprocessor 20, which then generates the operation command signal 7 and the frequency setting signal 8 and enters them into the transistorized inverter unit 1. Further, the frequency display device 4 converts the frequency setting signal 8 and the output frequency signal 9 into numerical values and displays the results of conversion. Also, the frequency shown on the frequency display device 4 is switched between the frequency setting signal 8 and the output frequency signal 9 by pressing the monitor switching key among the operation keys 30. Also, the operation command signal 7 is output after a direction of rotation has been designated by operation of the forward rotation and reverse rotation keys 30. Furthermore, the direction of rotation is shown by indicators (forward rotation indicator 5, reverse rotation indicator 6).
FIG. 11 shows the change of a set frequency at the time of pressing the operation key of the conventional inverter operation command apparatus, and the generation of the frequency setting signal 8 is described. While the increase key is being pressed, the frequency is increased. Specifically, 1 is continuously added to a current value of the frequency in order to reach a target value fast.
FIGS. 12 and 13 are flowcharts for the conventional increase/decrease key. Processing performed when the increase/decrease key is pressed will now be described with reference to FIGS. 12 and 13. At step S1, the key pressed is detected (in the figure, the .DELTA./.gradient. key indicates the increase/decrease key). If the .DELTA. key and .gradient. key are both off, the processing proceeds to step S8 (step S2). If either of the .DELTA. key or .gradient. key has been pressed, it is determined whether 0.5 seconds have elapsed since the addition or subtraction processing of the frequency has been performed. If the time elapsed is less than 0.5 seconds, the operation moves to step S8. If 0.5 seconds have elapsed, the processing advances to step S4 (step S3).
Step S4 is a variation calculation subroutine, in which a variation value is set according to a difference between a current frequency set value and an initial set value before the .DELTA./.gradient. key is pressed.
Subsequently, it is determined whether the key pressed is the .DELTA. key or the .gradient. key (step S5). If it is the .DELTA. key, the variation value is added to the frequency set value and the result of addition is defined as a new frequency set value (step S6). If the key pressed is the .gradient. key, the variation value is subtracted from the frequency set value and the result of subtraction is defined as a new frequency set value (step S7).
The frequency set value calculated as described above is displayed (step S8) and the processing returns to the start step.
FIG. 13 is a flowchart for the variation calculation subroutine, with which the variation calculation subroutine at step S4 will be described. It is determined whether the difference between the current frequency set value and the initial set value before the .DELTA./.gradient. key is pressed is greater than 1 Hz (step S101). If it is less than or equal to 1 Hz, 0.1 Hz is set as the variation value (step S103). If it is not less than 1 Hz, it is further determined whether the difference is greater than 10 Hz (step S102). If it is less than or equal to 10 Hz, 1 Hz is set as the variation value (step S104). If it is greater than 10 Hz, 10 Hz is set as the variation value (step S105). The variation value is thus set and the processing ends.
When the conventional inverter operation command apparatus, designed as described above, was used to set the frequency, especially to set a much larger or smaller value, the change of the frequency was so fast that the target value was exceeded and the increase or decrease key had to be pressed several times, resulting in a long setting time. Also, at least the forward rotation/reverse rotation and even stop keys had to be pressed to determine the direction of rotation and to run/stop the inverter. Further, the dedicated key had to be pressed to change the frequency display.